Pressurized steam cleaners and washers are utilized in a variety of situations for cleaning purposes. Such systems generally include a pair of tanks, one of which is for liquid cleanser or detergent and the other of which is for water. These tanks are connected to the inlet of a pump, usually through a mixer or aspirator which mixes the liquids in the desired ratios into a suitable cleaning solution, for discharge under pressure through the nozzle of a wand. Equipment of this type is controlled primarily by switching the pump on and then manipulating the wand as necessary to spray the object being cleaned.
Traditionally, such cleaning systems have utilized burners to heat the solution, however, such systems are best suited for applications where proper ventilation is available. Cleaning systems incorporating electrical heating elements have also been developed for use in hazardous areas such as grain elevators and the like, where a spark or open flame could trigger an explosion or fire. Such systems have been available from Sioux Steam Cleaner Corporation, the assignee hereof.
Although the electric cleaning systems of the prior art have functioned reasonably well, they have not been without certain difficulties. For example, purging of the air and priming of the system upon start-up are relatively timeconsuming in the systems of the prior art. This in turn can result in delays and erratic operation before the system is at full pressure. This can also cause flow discontinuities within the system which can result in overheating and damage to the equipment. In the case of cleaing systems with electrical heaters, it is especially important that the heating elements always be substantially immersed during operation to avoid uneven heating and thus premature burnout of the resistance elements. It is thus important to ensure that the entire system has been properly primed with liquid and purged of air to avoid possible overheating of the heating elements upon initial start-up, which in turn requires additional operator attention. Such cleaning systems are usually operated intermittently, and it will be appreciated that maintenance of adequate priming throughout the system has been a chronic problem. The parent application hereof to Sioux Steam Cleaner Corporation is directed to an electric combination cleaner which is adapted to effect complete and rapid priming of the system upon start-up, while being responsive to flow discontinuities which could damage the electrical heater elements. Although such cleaning systems can be designed to assure proper priming upon start-up, overheating can also occur upon shutdown or upon either start-up or shutdown if the system is operated improperly.
A need has thus arisen for a cleaner safety circuit by which certain control elements are automatically energized or de-energized after predetermined time delays to minimize the possibility of overheating upon start-up or shutdown, without reliance upon the operator.